Implantable lead with dissolvable coating for improved fixation and extraction

ABSTRACT

A cardiac rhythm management system provides an endocardial cardiac rhythm management lead with an at least partially dissolvable coating at least partially on insulating portions of the lead body at or near its distal end. Upon dissolution, the coating promotes tissue ingrowth to secure the lead in place within fragile vascular structures or elsewhere. Dissolution of one such coating releases a therapeutic agent, such as a steroid that modifies the fibrotic scar tissue content of tissue ingrowth, such that the resulting bond between the tissue and the lead is weak, so that the lead can be easily extracted if desired. One such lead includes an insulating elongate body carrying at least. The lead also includes an at least partially dissolvable coating on an insulating portion of the peripheral distal lead surface. The coating provides one or more of a rough surface, a porous surface, or a swollen surface after being exposed to an aqueous substance.

TECHNICAL FIELD

This invention relates generally to electrical leadwires andparticularly, but not by way of limitation, to a cardiac rhythmmanagement system providing an endocardial cardiac rhythm managementlead with an at least partially dissolvable coating on at least portionsof an insulating lead body for improved fixation and extraction.

When functioning properly, the human heart maintains its own intrinsicrhythm, and is capable of pumping adequate blood throughout the body'scirculatory system. However, some people have irregular cardiac rhythms,referred to as cardiac arrhythmias. Such arrhythmias result indiminished blood circulation. One mode of treating cardiac arrhythmiasuses drug therapy. Drugs are often effective at restoring normal heartrhythms. However, drug therapy is not always effective for treatingarrhythmias of certain patients. For such patients, an alternative modeof treatment is needed. One such alternative mode of treatment includesthe use of a cardiac rhythm management system. Such systems are oftenimplanted in the patient and deliver therapy to the heart.

Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via a transvenous leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering an high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock. The countershock interrupts the tachyarrhythmia, allowingthe heart to reestablish a normal rhythm for the efficient pumping ofblood. In addition to pacers, cardiac rhythm management systems alsoinclude, among other things, pacer/defibrillators that combine thefunctions of pacers and defibrillators, drug delivery devices, and anyother systems or devices for diagnosing or treating cardiac arrhythmias.

One aspect of typical cardiac rhythm management systems is providing anappropriate endocardial lead coupling an implantable cardiac rhythmmanagement device to the heart for sensing intrinsic electrical heartactivity signals and/or delivering electrical therapy such as pacingstimulations or defibrillation countershocks. In conventional cardiacrhythm management systems, the lead typically includes a distalelectrode that is transvenously guided into the right atrium or rightventricle. The electrode is carefully positioned to contact adjacentcardiac tissue for sensing and/or providing therapy. The preferredlocation provides adequate amplitude sensed intrinsic electrical heartactivity signals and low threshold energy requirements for effectivelydelivering pacing and/or defibrillation therapy. To ensure that theelectrode's location does not change over time in spite of continuousheart contractions, a fixation device may be used to anchor the distalend of the leadwire in position within the heart.

Even if the position of the electrode is stabilized, stimulationthresholds may vary over time as a result of interactions between theelectrode and the adjacent tissue. Fibrotic scar tissue may form duringthe recovery and healing process as the body reacts to the presence ofthe electrode. The growth of fibrotic tissue results in chronicstimulation energy thresholds that exceed the acute energy thresholdsobtained immediately after implant. As a result, higher stimulationenergies are required, thereby shortening the usable life of thebattery-powered implantable cardiac rhythm management device. Byproviding a steroid at the electrode and/or its associated fixationdevice, modified fibrotic tissue is formed and lower chronic stimulationthresholds are obtained, as disclosed in Heil, Jr. et al., U.S. Pat. No.4,819,661, which is assigned to the assignee of the present application,and which is incorporated herein by reference in its entirety.

Use of a fixation device to anchor the lead typically obtains consistentchronic sensing and stimulation thresholds, but such fixation devicescomplicate removal of the lead such as, for example, in the event of aninfection or lead failure. For example, removing a lead with a corkscrewor barb fixation device risks damage to the surrounding tissue to whichthe fixation device is firmly attached. Where such surrounding tissue isfibrotic scar tissue resulting from lead placement and fixation inconjunction with the normal healing process, separation of the lead fromthe surrounding scar tissue is even more difficult because the lead willlikely have become firmly incorporated within the body. Moreover, manysuch fixation devices are adapted only for securing the distal tip ofthe lead; they may not adequately secure ring electrodes that aredisposed at a slight distance away from the distal tip of the lead.Furthermore, most conventional fixation techniques are directed towardanchoring leads in the right side of the heart. Such techniques may notbe as well suited for anchoring leads elsewhere. Thus, there is a needfor providing a cardiac rhythm management lead that is capable of bothadequate fixation and removal. There is also a need for providing acardiac rhythm management lead that is capable of placement and fixationin other regions of the heart, such as within fragile vascularstructures.

SUMMARY

This document describes, among other things, a cardiac rhythm managementsystem providing an endocardial cardiac rhythm management lead with anat least partially dissolvable coating on at least portions of the leadbody at or near its distal end, which promotes tissue ingrowth to securethe lead in place within fragile vascular structures or elsewhere. Inone embodiment, dissolution of the coating releases a therapeutic agent.In a further embodiment, the therapeutic agent includes a steroid thatmodifies the fibrotic scar tissue component of tissue ingrowth, suchthat the resulting bond between the tissue and the lead is weak, suchthat the lead can be easily extracted if desired.

In one embodiment, the lead includes an insulating elongate body havinga proximal and a distal end and a peripheral surface. At least oneelongate electrical conductor, having a proximal end and a distal end,is carried within the elongate body. The conductor extendslongitudinally along substantially the entire length between theproximal and distal ends of the elongate body. At least one electrode islocated at or near the distal end of the elongate body. The electrode iscoupled to the distal end of the conductor. The lead also includes an atleast partially dissolvable coating on at least portions of theinsulating peripheral surface at or near the distal end of the elongatebody. The coating provides at least one of a rough surface, a poroussurface, and a swollen surface after being exposed to an aqueoussubstance. Other aspects of the invention will be apparent on readingthe following detailed description of the invention and viewing thedrawings that form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents.

FIG. 1 is a schematic drawing illustrating generally one embodiment ofportions of a cardiac rhythm management system and one environment inwhich it is used.

FIG. 2 is a schematic drawing illustrating generally one embodiment of adisposition of distal portions of a lead in a coronary sinus and/or agreat cardiac vein.

FIG. 3A is a schematic drawing illustrating one embodiment of portionsof a lead.

FIG. 3B is a schematic drawing illustrating the portions of the lead ofFIG. 3A after exposure to an aqueous substance.

FIG. 4A is a schematic drawing illustrating generally another embodimentof portions of a lead.

FIG. 4B is a schematic drawing illustrating the portions of the lead ofFIG. 4A after exposure to an aqueous substance.

FIG. 5A is a schematic drawing illustrating a further embodiment ofportions of a lead.

FIG. 5B is a schematic drawing illustrating the portions of the lead ofFIG. 5A after exposure to an aqueous substance.

FIG. 6 is a graph of steroid absorbance vs. time, illustrating generallytest results for a prototype embodiment of a lead.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents.

General Overview

This document describes, among other things, a cardiac rhythm managementsystem providing an endocardial cardiac rhythm management lead with anat least partially dissolvable coating on at least portions of aninsulating lead body, for improved fixation and extraction.

FIG. 1 is a schematic drawing illustrating generally, by way of example,but not by way of limitation, one embodiment of portions of a cardiacrhythm management system 100 and one environment in which it is used. InFIG. 1, system 100 includes an implantable cardiac rhythm managementdevice 105, which coupled via an intravascular endocardial lead 110 to aheart 115 of a human or other patient 120. System 100 also includes anexternal programmer 125 providing wireless communication with device105, such as by using a telemetry device 130. Lead 110 includes aproximal end 135, which is coupled to device 105, and a distal end 140,which is coupled on or about one or more portions of heart 115.

FIG. 2 is a schematic drawing illustrating generally, by way of example,but not by way of limitation, one embodiment of an exemplary dispositionof distal portions of lead 110. FIG. 2 illustrates chambers of heart115, including a right atrium 200, a right ventricle 205, a left atrium210, and a left ventricle 215. In the embodiment illustrated in FIG. 2,distal end 140 of lead 110 is transvenously guided into right atrium200, through a coronary sinus 220, and into a great cardiac vein 225.This example disposition of lead 110 is useful for delivering pacingand/or defibrillation energy to the left side of heart 115, such as fortreatment of congestive heart failure (CHF) or other cardiac disordersrequiring therapy delivered to the left side of heart 115. Otherpossible dispositions of distal portions of endocardial lead 110 includeinsertion into right atrium 200 and/or right ventricle 205, ortransarterial insertion into the left atrium 210 and/or left ventricle215.

FIG. 3A is a schematic drawing illustrating generally, by way ofexample, but not by way of limitation, one embodiment of portions oflead 110, including its distal end 140 and its proximal end 135. In thisembodiment, intravascular endocardial lead 110 includes a biocompatibleflexible insulating elongate body 300 (e.g., including a polymer such asmedical grade silicone rubber) for translumenal (i.e., transvenous ortransarterial) insertion and access within a living organism such aspatient 120. In one embodiment, slender elongate body 300 is tubular andhas a peripheral outer surface of diameter d that is small enough fortranslumenal insertion into coronary sinus 220 and/or great cardiac vein225. An elongate electrical conductor 305 is carried within insulatingelongate body 300. Conductor 305 extends substantially along the entirelength between the distal end 140 and proximal end 135 of lead 110, andthis length is long enough for lead 110 to couple device 105, which isimplanted pectorally, abdominally, or elsewhere, to desired locationswithin heart 115 for sensing intrinsic electrical heart activity signalsor providing pacing/defibrillation-type therapy thereto. Elongate body300 forms an insulating sheath covering around conductor 305. Conductor305 is coupled to an electrode 310 at or near distal end 140 of elongatebody 300. Conductor 305 is coupled to a connector 315 at or nearproximal end 135 of elongate body 300. Device 105 includes a receptaclefor receiving connector 315, thereby obtaining electrical continuitybetween electrode 310 and device 105.

Electrode 310, or at least a portion thereof, is not covered by theinsulating sheath of elongate body 300. The embodiment of FIG. 3Aincludes a ring or ringlike electrode 310 that provides an exposedelectrically conductive surface around all, or at least part of, thecircumference of lead 110. In one embodiment, the exposed surface ofelectrode 310 is smooth. In another embodiment, the exposed surface ofelectrode 310 is not smooth, thereby allowing tissue ingrowth intointerstitial spaces of electrode 310. In one example, electrode 310 is acoiled wire electrode that is wound around the circumferential outersurface of lead 110. Lead 110 also includes other configurations,shapes, and structures of electrode 310.

Lead 110 includes a biocompatible coating 320 on at least one insulatingportion of the peripheral surface of elongate body 300 at or near distalend 140. In one embodiment, as illustrated in FIG. 3A, coating 320extends circumferentially completely (or at least partially) around thetubular outer peripheral surface of lead 110. In the embodiment of FIG.3A, coating 320 occupies one or more nonelectrode regions (i.e.,insulating portions of the lead body) extending along a length l fromthe tip of distal end 140 of lead 110, where length l is approximatelyequal to a distance within coronary sinus 220 and great cardiac vein 140into which distal end 140 of lead 110 is inserted. In a furtherembodiment, coating 320 also overlaps one or more portions of one ormore electrodes, such as electrode 310, providing an insulating coveringthat reduces the exposed surface area of the electrode 310.

According to one aspect of the invention, coating 320 is at leastpartially dissolvable when exposed to an aqueous substance such as bloodor bodily fluids. In one embodiment, coating 320 provides asubstantially smooth low friction outer surface before dissolution ofportions of coating 320. After being exposed to an aqueous substance,however, portions of coating 320 dissolve. According to one aspect ofthe present system, this dissolution initially makes distal end 140 oflead 110 more slippery, making it easier to insert into patient 120.After portions of coating 320 dissolve, remaining substrate portions ofcoating 320 provide a rough and/or porous surface (as illustrated inFIG. 3B) that promotes tissue ingrowth into resulting interstitialregions. Such tissue ingrowth anchors and/or secures lead 110 toadjacent cardiac tissue, such as within coronary sinus 220 and/or greatcardiac vein 225, or elsewhere in or about heart 115. In one embodiment,portions of coating 320 undergo osmotic swelling after being exposed tothe aqueous substance. This further assists in securing lead 110 withina vascular region such as, for example, within coronary sinus 220 and/orgreat cardiac vein 225. Thus, in one embodiment, coating 320 includes aplurality of substantially soluble particles dispersed in asubstantially insoluble medium that is adhered to portions of elongatebody 300 at or near distal end 140. When exposed to an aqueousenvironment, the substantially soluble particles dissolve, leavingbehind a rough and/or porous surface that results in tissue ingrowthand/or osmotic swelling, which promotes lead fixation that isparticularly well-suited for vascular structures.

In another embodiment, coating 320 includes a therapeutic agent such as,by way of example, but not by way of limitation, a drug, a steroid, acorticosteroid, an antibiotic, and/or an antirejection agent. In oneexample, the therapeutic agent is provided by the substantially solubleparticles that are dispersed in the substantially insoluble medium. Inone example, coating 320 includes substantially soluble particles of asteroid such as dexamethasone acetate. When coating 320 is exposed to anaqueous environment, the substantially soluble steroid elementsdissolve, providing sustained release into the surrounding tissue. Thisdelays local protein synthesis and tissue healing, which modifies theformation of normal fibrotic scar tissue during the recovery and healingprocess. As a result, a lesser amount of strongly-bound fibrotic tissueis formed during tissue ingrowth into interstices provided by the roughand/or porous surface of the remaining insoluble portion of coating 320.The resulting ingrown tissue promotes adequate anchoring and fixation oflead 110. Because the ingrown tissue includes modified fibrotic scartissue, however, it is easier to separate lead 110 from the surroundingtissue by pulling and/or turning the lead 110 during removal. Stateddifferently, steroid release from the structure receiving tissueingrowth on an insulating portion of elongate body 300 results infriable tissue ingrowth that is more easily disrupted or separated fromlead 110 upon extraction and removal of lead 110. Thus, lead 110 offersadvantages for both its fixation and removal. Furthermore, reducedpacing and defibrillation threshold energies may be obtained byproviding the therapeutic agent near electrode regions, as discussedabove.

In a further embodiment, coating 320 provides a therapeutic agentincluding more substantially soluble dexamethasone sodium phosphateparticles. These particles are dispersed in a substantially insolublemedium, such as biocompatible silicone rubber medical adhesive, otherpolymer, or other suitable biocompatible adhesive substance. Siliconerubber medical adhesive is permeable by water vapor. As a result, watervapor can reach interior dry pockets of the dispersed soluble particles,allowing such particles to dissolve and be released from coating 320into the surrounding tissue. Other biocompatible, water vapor permeable,and substantially insoluble adhesive or polymeric media can also beused.

In another embodiment, coating 320 provides a therapeutic agentincluding more substantially soluble dexamethasone sodium phosphateelements dispersed in the substantially insoluble silicone rubbermedical adhesive. This embodiment advantageously provides both friabletissue encapsulation and osmotic swelling.

In yet another embodiment, smooth coating 320 includes a combination ofthe therapeutically active agents, such as dexamethasone acetate anddexamethasone sodium phosphate, dispersed in the substantially insolublemedium (e.g., silicone rubber). In this embodiment, upon exposure tobodily fluids, rapid initial release of the dexamethasone drug substanceoccurs predominantly in the form of the more soluble dexamethasonesodium phosphate. Release of the dexamethasone drug substance in theform of dexamethasone acetate also occurs upon exposure to bodilyfluids, but does so more slowly. Dissolution and release of thedexamethasone sodium phosphate phase will also result in the developmentof porous surface structures into which tissue ingrowth can occur.Release of the combined forms of the steroid will also serve to modifythe tissue ingrowth producing friable encapsulation.

In yet another embodiment, smooth coating 320 includes a combination ofthe therapeutically active agent dexamethasone acetate and a moresubstantially soluble nontherapeutic inert agent, such as mannitol orglycerol. In this embodiment, upon exposure to bodily fluids, both theactive and inert agents dissolve. The more substantially soluble inertagent first aids in the initial implantation, by lowering lead frictionand making the lead more slippery. Then the inert agent quicklydissolves to generate porous features on the surface of the lead body.Release of the dexamethasone drug substance in the form of dexamethasoneacetate also occurs upon exposure to bodily fluids, but does so moreslowly, as described above. Release of these combined forms of activeand inert additives again serves to modify the tissue ingrowth,providing friable encapsulation.

During manufacture, at least one insulating portion of elongate body 300is coated with coating 320. The coating 320 cures such that it adheresto elongate body 300. Increasing the percentage of soluble particlesdispersed in the insoluble medium results in increased roughening and/orporosity after lead 110 is exposed to an aqueous substance during use.However, the percentage of soluble particles dispersed in the insolublemedium is typically not so great as to diminish the adhesive propertiesof coating 320 or to diminish the integrity of coating 320 after itspartial dissolution during its use. In a first embodiment, coating 320includes up to 40% soluble particles (e.g., dexamethasone, dexamethasoneacetate or dexamethasone sodium phosphate) combined with or dispersed inthe insoluble medium (e.g., silicone rubber medical adhesive). In asecond embodiment, coating 320 includes up to 35% soluble particles(e.g., dexamethasone, dexamethasone acetate or dexamethasone sodiumphosphate) combined with or dispersed in the insoluble medium (e.g.,silicone rubber medical adhesive). In a third embodiment, coating 320includes up to 30% soluble particles (e.g., dexamethasone, dexamethasoneacetate or dexamethasone sodium phosphate) combined with or dispersed inthe insoluble medium (e.g., silicone rubber medical adhesive). In afourth embodiment, coating 320 includes between 30%-40% solubleparticles (e.g., dexamethasone, dexamethasone acetate or dexamethasonesodium phosphate) combined with or dispersed in the insoluble medium(e.g., silicone rubber medical adhesive).

FIG. 4A is a schematic drawing illustrating generally, by way ofexample, but not by way of limitation, another embodiment of lead 110,which is similar in many respects to the embodiment of lead 110described with respect to FIG. 3A. The embodiment of FIG. 4A includes aplurality of electrodes, such as ring electrodes 310A-C, and tipelectrode 400 at distal end 140 of lead 110. The electrodes 310A-C and400 are coupled to proximal end 135, such as by a correspondingplurality of conductors 305A-D interconnecting electrodes 310A-C and 400to individual connectors 315 that are received at correspondingreceptacles on device 105. Alternatively, one or more of electrodes310A-C is tied to one or more others of electrodes 310A-C using one ormore shared/common conductors 305A-D.

Interelectrode portions of insulating elongate body 300 of lead 110 arecovered with coatings 320A-C, which are at least partially dissolvedduring use as described above, as illustrated in FIG. 4B. In oneembodiment, coatings 320A-C elute steroids or other therapeutic agentsduring dissolution, as discussed above. In a further embodiment, one ormore of coatings 320A-C also overlap one or more portions of one or moreadjacent electrodes, providing an insulating covering that reduces theexposed surface area of the partially covered electrode. The embodimentof FIGS. 4A-B also optionally include one or more additional passive oractive fixations devices, such as one or more tines 405A-B extendinglaterally outward from a portion of elongate body 300 at or near tipelectrode 400. In one example, tines 405A-B are formed of the sameinsulating material as elongate body 300.

FIG. 5A is a schematic drawing illustrating generally, by way ofexample, but not by way of limitation, another embodiment of lead 110,which is similar in many respects to the embodiment of lead 110described with respect to FIG. 4A. The embodiment of FIG. 5A includesone or more electrodes, such as coil electrodes 310A-B, which eachinclude wires wound around the peripheral circumference of elongate body300. Coil electrodes 310A-B provide a nonuniform, rough peripheralsurfaces that allow tissue ingrowth into interstitial regions betweenthe individual coil windings for providing improved fixation.Interelectrode coating 320A partially dissolves after implantation, asdiscussed above, which also allows tissue ingrowth into thesubstantially insoluble substrate portion of interelectrode coating320A, as illustrated in FIG. 5B. In one embodiment, coating 320Areleases a therapeutic agent during dissolution, such as a steroid thatmodifies the fibrotic scarring content of the tissue ingrowth into therough/porous substrate portion of coating 320A. The steroid elution fromcoating 320A also modifies the fibrotic scar tissue content of thetissue that grows into the nearby interstices of electrodes 310A-B. Theresulting ingrown tissue is friable. It provides fixation of lead 110,but allows easier lead extraction. In a further embodiment, coating 320Aalso overlaps one or more portions of one or more electrodes, providingan insulating covering that reduces the exposed surface area of thepartially covered electrode. FIG. 5A also illustrates an embodiment oflead 110 that includes optional other fixation mechanisms, such as oneor more of mesh tip electrode 400 or a helical anchor 500 extendinglongitudinally outward from tip electrode 400. It is understood that oneor more of these or other like fixation mechanisms can be used eitheralone, or in combination with each other, as desired.

FIG. 6 is a graph of steroid absorbance vs. time, illustratinggenerally, by way of example, but not by way of limitation, test resultsfor a prototype embodiment of lead 110, which is similar to thatillustrated in FIG. 4A, but including a single tip electrode and 4 ringelectrodes. The electrodes were separated by polymeric interelectroderegions coated with silicone rubber medical adhesive that includedapproximately 10% dexamethasone acetate. Approximately 1.8 milligrams ofdexamethasone acetate was released over a period of approximately oneweek, with some drug release still continuing at one week after exposureto an aqueous solution as indicated by the slight positive slope of thecurve in FIG. 6 at that time. In one embodiment, the time period duringwhich the therapeutic agent is released is optimized by proper selectionof its aqueous solubility, or by otherwise selecting the appropriatecombination of the substantially soluble therapeutic agent, thesubstantially insoluble binder medium, and an appropriate inertadditive.

CONCLUSION

The above-described system provides, among other things, a cardiacrhythm management system providing an endocardial cardiac rhythmmanagement lead with an at least partially dissolvable coating oninsulating portions of the lead body at or near its distal end, whichpromotes tissue ingrowth to secure the lead in place. In one embodiment,dissolution of the coating releases a therapeutic agent. In a furtherembodiment, the therapeutic agent includes a steroid that modifies thefibrotic scar tissue content of tissue ingrowth, such that the resultingbond between the tissue and the lead is weak, such that the lead can beeasily extracted if desired.

Although the present cardiac rhythm management system is described abovewith respect to a lead that is disposed within the vasculature of acoronary sinus and/or a great cardiac vein, it is understood that theendocardial lead can be positioned elsewhere within the heart, such aswithin the right or left atria or ventricles, within other bloodvessels, or elsewhere.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An intravascular lead, the lead including: aninsulating elongate body having a proximal and a distal end and aperipheral surface; at least one elongate electrical conductor, having aproximal end and a distal end, the conductor carried within the elongatebody and extending longitudinally along substantially the entire lengthbetween the proximal and distal ends of the elongate body; at least oneelectrode located at or near the distal end of the elongate body, theelectrode being coupled to the distal end of the conductor; and an atleast partially dissolvable coating at least partially on an insulatingportion of the peripheral surface at or near the distal end of theelongate body, the coating providing at least one of a rough surface, aporous surface after being exposed to an aqueous substance.
 2. The leadof claim 1, in which the coating provides a substantially smooth surfacebefore being exposed to the aqueous substance.
 3. The lead of claim 2,in which the coating includes a plurality of substantially solubleparticles dispersed in a substantially insoluble medium.
 4. The lead ofclaim 3, in which the insoluble medium is adhered to an insulatingportion of the elongate body.
 5. The lead of claim 4, in which thesoluble particles include a therapeutic agent.
 6. The lead of claim 5,in which the therapeutic agent includes at least one of a drug, asteroid, a corticosteroid, an antibiotic, and an antirejection agent. 7.The lead of claim 5, in which the therapeutic agent includes one ofdexamethasone acetate and dexamethasone sodium phosphate.
 8. The lead ofclaim 5, in which the insoluble medium includes a biocompatible medicaladhesive.
 9. The lead of claim 8, in which the medical adhesive includessilicone.
 10. An intravascular lead, the lead including: an insulatingelongate body having a proximal and a distal end and a peripheralsurface; at least one elongate electrical conductor, having a proximalend and a distal end, the conductor carried within the elongate body andextending longitudinally along substantially the entire length betweenthe proximal and distal ends of the elongate body; at least oneelectrode located at or near the distal end of the elongate body, theelectrode being coupled to the distal end of the conductor; and an atleast partially dissolvable coating at least partially on an insulatingportion of the peripheral surface at or near the distal end of theelongate body, the coating providing at least one of a rough surface, aporous surface, and a swollen surface after being exposed to an aqueoussubstance; in which the coating also covers at least part of the atleast one electrode.
 11. The lead of claim 1, in which the coatingincludes a therapeutic agent that promotes friable tissue associatedwith the insulating portion of the peripheral surface of the lead foreasier lead removal.
 12. An intravascular lead for providing cardiacrhythm management therapy, the lead including: a flexible insulatingelongate body having a proximal and a distal end and a peripheralsurface; a plurality of elongate electrical conductors, each conductorhaving a proximal end and a distal end, each conductor carried withinthe elongate body and extending longitudinally along substantially theentire length between the proximal and distal ends of the elongate body;a plurality of electrodes located at or near the distal end of theelongate body, each electrode being coupled to the distal end of atleast one of the conductors; and a partially dissolvable coating atleast partially on an insulating portion of the peripheral surface at ornear the distal end of the elongate body, the coating providing at leastone of a rough surface, a porous surface, and a swollen surface afterbeing exposed to an aqueous substance, the coating including a pluralityof substantially soluble particles dispersed in a substantiallyinsoluble silicone adhesive that is bonded to the insulating elongatebody, and in which the substantially soluble particles are selected fromthe group consisting of dexamethasone, dexamethasone acetate anddexamethasone sodium phosphate.
 13. The lead of claim 12, in which thecoating includes up to 40% substantially soluble particles dispersed inthe adhesive.
 14. The lead of claim 12, in which the coating includes upto 35% substantially soluble particles dispersed in the adhesive. 15.The lead of claim 12, in which the coating includes up to 30%substantially soluble particles dispersed in the adhesive.
 16. The leadof claim 12, in which the coating also covers at least part of at leastone of the electrodes.
 17. An intravascular lead for providing cardiacrhythm management therapy, the lead including: a flexible insulatingelongate body having a proximal and a distal end and a peripheralsurface; a plurality of elongate electrical conductors, each conductorhaving a proximal end and a distal end, each conductor carried withinthe elongate body and extending longitudinally along substantially theentire length between the proximal and distal ends of the elongate body;a plurality of electrodes located at or near the distal end of theelongate body, each electrode being coupled to the distal end of at oneof the conductors; and a means for performing the functions of coatingan insulating portion of the peripheral surface at or near the distalend of the elongate body, providing at least one of a rough surface, aporous surface, and a swollen surface, after being exposed to an aqueoussubstance, for fixation of tissue thereto.
 18. A cardiac rhythmmanagement system, including: an electronics unit; and a lead coupled tothe electronics unit, the lead including: an insulating elongate bodyhaving a proximal and a distal end and a peripheral surface; at leastone elongate electrical conductor, having a proximal end and a distalend, the conductor carried within the elongate body and extendinglongitudinally along substantially the entire length between theproximal and distal ends of the elongate body; at least one electrodelocated at or near the distal end of the elongate body, the electrodebeing coupled to the distal end of the conductor; and an at leastpartially dissolvable coating at least partially on an insulatingportion of the peripheral surface at or near the distal end of theelongate body, the coating providing at least one of a rough surface, aporous surface, after being exposed to an aqueous substance.
 19. Amethod of providing cardiac rhythm management therapy, the methodincluding: translumenally disposing a lead in a heart; exposing the leadto an aqueous substance; partially dissolving a coating at leastpartially on an insulating portion of the lead to provide at least oneof a rough surface, a porous surface, and a swollen surface, therebypromoting tissue ingrowth.
 20. The method of claim 19, in whichdisposing the lead includes disposing the lead in at east one of a rightatrium and a right ventricle of the heart.
 21. The method of claim 19,in which disposing the lead includes disposing the lead in at least oneof a coronary sinus and a great cardiac vein of the heart.
 22. Themethod of claim 19, in which partially dissolving the coating includesreleasing a therapeutic agent.
 23. The method of claim 22, in whichreleasing the therapeutic agent includes releasing at least one of adrug, a steroid, a corticosteroid, an antibiotic, and an antirejectionagent.
 24. The method of claim 23, in which releasing the therapeuticagent includes releasing at least one of dexamethasone, dexamethasoneacetate, and dexamethasone sodium phosphate.
 25. The method of claim 19,in which dissolving the coating includes releasing a therapeutic agentthat promotes friable tissue associated with the insulating portion ofthe peripheral surface of the lead for easier lead removal.
 26. A methodof forming a leadwire, the method comprising: forming at least oneelongate electrical conductor, having a proximal end and a distal end;forming at least one electrode at and coupled to a distal end of theconductor; forming an insulating elongate body covering substantiallyall of the conductor and leaving exposed at least a portion of theelectrode; coating portions of the insulating elongate body near thedistal end of the conductor with an at least partially dissolvablecoating, the coating providing at least one of a rough surface, a poroussurface, and a swollen surface after being exposed to an aqueoussubstance.
 27. The method of claim 26, in which coating includesapplying a medium carrying soluble elements.
 28. The method of claim 27,in which coating further includes applying biocompatible siliconeadhesive carrying a steroid.
 29. The method of claim 28, in whichcoating further includes applying biocompatible silicone adhesiveincluding at least one of dexamethasone, dexamethasone acetate, anddexamethasone sodium phosphate.
 30. The method of claim 27, in whichcoating includes applying biocompatible silicone adhesive including upto 40% of at least one of dexamethasone, dexamethasone acetate, anddexamethasone sodium phosphate.
 31. The method of claim 27, in whichcoating includes applying biocompatible silicone adhesive including upto 35% of at least one of dexamethasone, dexamethasone acetate, anddexamethasone sodium phosphate.
 32. The method of claim 27, in whichcoating includes applying biocompatible silicone adhesive including upto 30% of at least one of dexamethasone, dexamethasone acetate, anddexamethasone sodium phosphate.
 33. The method of claim 27, in whichcoating includes applying biocompatible silicone adhesive includingbetween 30% and 40% of at least one of dexamethasone, dexamethasoneacetate, and dexamethasone sodium phosphate.
 34. The method of claim 26,further including coating a portion of the electrode with the at leastpartially dissolvable coating.
 35. The method of claim 26, in whichcoating portions of the insulating elongate body includes providing atherapeutic agent that, upon at least partial dissolution of thecoating, provides friable tissue associated with the insulating portionof the peripheral surface of the lead for easier lead removal.
 36. Thelead of claim 1, in which the coating also covers at least part of theat least one electrode.
 37. An intravascular lead, the lead including:an elongate body extending from a proximal and a distal end, and havingan intermediate portion therebetween, the elongate body having an outerperipheral surface; at least one elongate electrical conductor carriedwithin the elongate body and extending longitudinally alongsubstantially the entire length between the proximal and distal ends ofthe elongate body; at least one electrode located at or near the distalend of the elongate body, the electrode being coupled to the distal endof the conductor; and an at least partially dissolvable coating at leastpartially on an insulating portion of the outer peripheral surface atthe intermediate portion of the body, the coating providing a swollensurface after being exposed to an aqueous substance, the coatingconfigured to directly contact tissue.
 38. The lead of claim 37, inwhich the coating provides a substantially smooth surface before beingexposed to the aqueous substance.
 39. The lead of claim 37, wherein thecoating is disposed directly adjacent to the at least one electrode. 40.The lead of claim 37, in which the coating also covers at least part ofthe at least one electrode.
 41. The lead of claim 37, in which thecoating includes a therapeutic agent that promotes friable tissueassociated with the insulating portion of the peripheral surface of thelead for easier lead removal.